In a transmissive image display apparatus such as a liquid crystal display apparatus, a direct surface light source device may be used as a backlight. In recent years, a direct surface light source device that includes plural light emitting elements as a light source has been used.
For example, a direct surface light source device includes a substrate, plural light emitting elements, plural light flux controlling members and a light diffusion member. The plural light emitting elements are arranged on the substrate in a matrix shape. The light flux controlling member that spreads light emitted from each light emitting element in a surface direction of the substrate is disposed above each light emitting element. The light emitted from the light flux controlling member is diffused by the light diffusion member and planarly illuminates an illuminated member (liquid crystal panel, for example) (see Japanese Patent Application Laid-Open No. 2006-114863, for example).
FIGS. 1A and 1B are diagrams illustrating a surface light source device related to Japanese Patent Application Laid-Open No. 2006-114863. FIG. 1A is a cross-sectional view and a view of an optical path of the surface light source device in a case where there is no gap between a substrate and a light flux controlling member. FIG. 1B is a cross-sectional view and a view of an optical path of the surface light source device in a case where there is a gap between the substrate and the light flux controlling member. As shown in FIG. 1A, surface light source device 10 related to Japanese Patent Application Laid-Open No. 2006-114863 includes substrate 20, light emitting element 30 (light emitting chip) that is disposed on substrate 20, light flux controlling member 40 (lens) that is disposed on substrate 20 without a gap to cover light emitting element 30 and controls distribution of light emitted from light emitting element 30, and light diffusion member 50 that transmits the light emitted from light flux controlling member 40 while diffusing the light. Light flux controlling member 40 includes incidence surface 42 on which the light emitted from light emitting element 30 is incident, emission surface 44 through which the light incident on incidence surface 42 is emitted to the outside, and rear surface 46 that is formed on a side opposite to emission surface 44.
As shown in FIG. 1A, the light emitted from light emitting element 30 enters light flux controlling member 40 through incidence surface 42. The light that enters light flux controlling member 40 reaches emission surface 44 and is then emitted to the outside through emission surface 44. Here, the light is refracted by the shape of emission surface 44 and approximately uniformly irradiates light diffusion member 50.